The present invention relates generally to an ion propulsion system, and in particular to a method and apparatus for igniting a plasma in an ion propulsion system.
For over thirty years, ion engines have been proposed for propulsion of vehicles in space. Outside of space propulsion, ion generation may also be applied to various types of materials processing systems involving ion sources, such as for ion beam etching or micromachining. Ion engines use movement of ions to provide thrust.
Generally, an ion engine has an ion accelerator system that uses an anode, a cathode, a screen grid and an accelerator grid coupled within a thruster housing. Generally, an ion engine works by generating an inert gas plasma within the thruster housing. Xenon is an example of a suitable gas. A charge within the plasma between the anode and cathode forms ions. The inert gas ions leave the thruster through the charged screen and accelerator. The net force from the ions leaving the thruster housing generates a thrust. A neutralizer is located outside the thruster housing and generates electrons. The electrons are attracted to the ions so the ions do not re-enter the thruster housing as they otherwise would in space.
To initiate a breakdown of the xenon to form ions in the thruster or electrons at the neutralizer a high voltage breakdown must occur between the anode and cathode. Previously, it was thought that separate power supplies must be used to initiate the high voltage breakdown at both the thruster and the neutralizer.
In spacecraft design, it is desirable to eliminate parts and complexity when possible. More parts increases weight of the spacecraft. More parts and complexity inherently reduces reliability.
It is therefore an object of the invention to provide a power supply system that operates reliably and reduces overall weight and complexity.
It is therefore one object of the invention to provide a starter circuit that operates reliably and reduces overall weight of the spacecraft.
In one aspect of the invention, a starter circuit includes a power supply having an output inductor with a tap. A switch is coupled to the tap. The switch has a control input. A pulse control logic circuit is coupled to said control input, said pulse control logic circuit controlling said switch to an off state to generate a high voltage discharge.
In a further aspect of the invention, a method of starting plasma includes the steps of:
emitting a gas;
charging an inductor having a tap and an output;
coupling a starter circuit to said tap;
controlling the starter circuit to initiate a high voltage discharge;
producing a current through the gas;
establishing a plasma; and
igniting the plasma.
Another advantage of the invention is that the because a pulse input is used rather than a continuous source a high voltage rectifier and regulation control circuit are not required.
One advantage of the invention is a separate power supply for the starter circuit has been eliminated from the spacecraft. This reduces weight and complexity.
Other features and advantages of the invention are readily apparent from the following detailed description of carrying out the invention when taken in connection with the accompanying drawings.